Evaluation Of Chang 7-Chang 9 Source Rocks And Oil Source Research In Zhoujiawan-Gaoqiao Area Of ??Ordos Basin

The lower Yanchang Formation in Ordos Basin exists in a well-potential exploration.the large oil fields in Jingbian and Ansai have been found.Nowadays hydrocarbon source rock in the Yanchang Formation of the Triassic Period is dominated by Chang 7,however,dark mudstone exist in the Chang 8 and Chang 9 under the investigation.Therefore this paper,based on the core observation,logging and the profile and plane distribution of mudstone,identifys the logging identification standards in different layers of mudstone and extension,and spatial distribution and extension of mudstone.On this basis,Under the analysis of rock pyrolysis,organic carbon determination,vitrinite group separation,isotopic determination and GC-MS analysis,the hydrocarbon potential of Chang 7,Chang8 and Chang 9 source rocks,and a clear image for regional source rocks and crude oils in different geochemical characteristics of different layers,is determined,by this judging sources of crude oil in two different region of Gaoqiao and Zhoujiawan.Study on hydrocarbon source rocks show that Chang 7,Chang 8 and Chang 9 source rocks are characterized by supply ability of hydrocarbon,but there are differences of strength of supplying hydrocarbon between the different study areas and different layers.Chang 7,Chang 8 and Chang 9 source rocks have reached a mature stage of hydrocarbon generation,and have the characteristics of high abundance of organic matter and the type of organic matter.In the west region of Zhoujiawan,Chang 7 source rock is widely distributed,compared with Chang 9 and Chang 8 source rocks,and the distribution of mudstone in Chang 8 is narrow and thin.In terms of the capacity of generating oil and gas,Chang 7 source rock is stronger,Chang 8 weaker,Chang 9 weakest.In the east region of Gaoqiao,Chang 9 source rock has a wide distribution,in contrast with Chang 7 and Chang 8 source rocks,and the distribution of mudstone in Chang 8 is narrow and thin.In the aspect of the capacity of generating oil and gas,Chang 9 source rock is stronger,Chang 7 weaker,Chang 8 weakest.Under the comparison of various geochemical parameters of source rocks and crude oil in Chang 7,Chang 8 and Chang 9,the hydrocarbon source rocks and oil Ts,C₃₀ Diahopane and C₃₀ hopanes are selected as parameters of oil source correlation owing to the the different divergence and stability.The result of each layer of oil source correlation in the study shows Chang 81 crude oil mainly comes from Chang 7 source rock in the west region,where the relative content of tricyclic terpanes,C₃₀ rearrangement hopane and Ts is relatively low,with C₃₀ hopanes as the main peak,and Ts/C₃₀ hopane ranges from 0.27 to 0.37 and C₃₀ Diahopane/C₃₀ hopane from 0.13 to 0.26.As for the oil of Chang 82 and Chang 9 in the west area,it comes from the adjacent source rock,in which the content of Ts,C₃₀ and C₃₀ rearranged hopane is generally higher,showing "V" type and being the peak for C₃₀ hopane,and TS/C₃₀ hopane ranges from 0.48 to 1.15 and C₃₀ Diahopane/C₃₀ hopane from 0.42 to 0.68.in contrast with the west region,the crude oil from Chang 8 and Chang 9 source rocks largely come from the top segment of Chang 9 source rocks,in which the C₃₀ rearranged hopane and Ts content is generally higher,Ts/C₃₀ hopane ranges from 0.89 to 4.5 and C₃₀ Diahopane/C₃₀ hopane from 0.65 to 4.72,with an average of 1.85 and without the main peak of C₃₀ hopane.